The aim of this project is to characterize the unfolding of individual differences in relation to behavioral and stress reactivity and maternal-infant interactions during early childhood development in infants born to women at high risk for depression. We will focus on the emergence of these differences in reactivity both at the behavioral level, and with respect to development of neuroendocrine differences that accompany these distinct patterns of behavior. We propose to facilitate the development of translational research in considering these issues by: 1) providing an environment for collegial interaction; 2) developing home-based behavioral protocols that will facilitate the understanding of influences of personal and social factors; 3) creating a database infrastructure that would facilitate statistical approaches for analyzing individual change in mental health and multilevel influences in a developmental context; 4) applying state-of- the-art methodologies for the study of change over time of infant neuroendocrine functioning and its relationship to change over time of maternal infant social interrelation; and 5) promoting translational research activities for pre-doctoral students and postdoctoral fellows through participation in the research project proposed here, and in coordination with existing training programs in developmental and clinical psychology, pediatrics, social work, and psychiatry. Our research project is unique in that it proposes to identify pregnant females at risk for depression, then study the mother and their offspring once born using a longitudinal approach. We will attempt to elucidate different developmental trajectories in the function of the limbic hypothalamic-pituitary-adrenal (LHPA) system, contingent on maternal-infant social interactions, which may explain different mental health outcomes. We will also determine whether there is an early and recognizable biological vulnerability in infants who later develop psychopathology. We will evaluate moderators of these relationships, and relate them to the dynamic bidirectionality of behavior and biological processes, keeping in perspective the infant's development. This developmental study will ultimately lead to future funding, as we further our understanding of individual differences in the development of mental illness, and define working models that will guide the design of preventive interventions.